Life expectancy in the United States has been in decline for the first time in decades, and public health officials have identified a litany of potential causes, including inaccessible health care, rising drug addiction and rates of mental health disorders, and socio-economic factors. But disentangling these variables and assessing their relative impact has been difficult.
Now, a multi-institution study led by the Yale School of Medicine and University of Alabama-Birmingham has attempted to tease out the relative impact of two variables most often linked to life expectancy -- race and education -- by combing through data about 5,114 black and white individuals in four U.S. cities.
The lives and deaths among this group of people -- who were recruited for a longevity study approximately 30 years ago, when they were in their early 20s, and are now in their mid-50s -- shows that the level of education, and not race, is the best predictor of who will live the longest, researchers report Feb. 20 in the American Journal of Public Health. The individuals were part of the Coronary Artery Risk Development in Young Adults (CARDIA) study.
Among the 5,114 people followed in the study, 395 had died.
"These deaths are occurring in working-age people, often with children, before the age of 60," said Yale's Brita Roy, assistant professor of medicine and epidemiology and corresponding author of the paper.
The rates of death among individuals in this group did clearly show racial differences, with approximately 9% of blacks dying at an early age compared to 6% of whites. There were also differences in causes of death by race. For instance, black men were significantly more likely to die by homicide and white men from AIDS. The most common causes of death across all groups over time were cardiovascular disease and cancer.
But there were also notable differences in rates of death by education level. Approximately 13% of participants with a high school degree or less education died compared with only approximately 5% of college graduates.
Strikingly, note the researchers, when looking at race and education at the same time, differences related to race all but disappeared: 13.5% of black subjects and 13.2% of white subjects with a high school degree or less died during the course of the study. By contrast, 5.9% of black subjects and 4.3% of whites with college degrees had died.
To help account for differences in age-related mortality, the researchers used a measure called Years of Potential Life Lost (YPLL), calculated as projected life expectancy minus actual age at death. This measure not only captures numbers of deaths, but also how untimely they were. For example, someone who dies at age 25 from homicide accrues more YPLL than someone who dies at age 50 from cardiovascular disease. It would take two deaths at age 50 to equal the YPLL from a single death at age 25.
Even after accounting for the effects of other variables such as income, level of education was still the best predictor of YPLL. Each educational step obtained led to 1.37 fewer years of lost life expectancy, the study showed.
"These findings are powerful," Roy said. "They suggest that improving equity in access to and quality of education is something tangible that can help reverse this troubling trend in reduction of life expectancy among middle-aged adults."